At present, the most of the manufacture factories is equipped with the online monitoring system of the waste water pollution source. The self-priming pump is used in the online monitoring system to perform water quality sampling to the pollution source according to prior art. For that the self-priming pump must normally work, it needs enough water in the sample pipe connected with the self-priming pump. In the drain process of the large amount of the industry waste water, the bacteria growth phenomenon occurs to the waste water flowing through the sample pipe check valve, and may easily cause that the check valve is blocked and cannot be deactivated, and then the sample pipe loses the water. Thus, the self-priming pump cannot normally work. Then, it results in that the monitoring data of the online monitor is not normal.